20,618 research outputs found
The extended gaussian ensemble and metastabilities in the Blume-Capel model
The Blume-Capel model with infinite-range interactions presents analytical
solutions in both canonical and microcanonical ensembles and therefore, its
phase diagram is known in both ensembles. This model exhibits nonequivalent
solutions and the microcanonical thermodynamical features present peculiar
behaviors like nonconcave entropy, negative specific heat, and a jump in the
thermodynamical temperature. Examples of nonequivalent ensembles are in general
related to systems with long-range interactions that undergo canonical
first-order phase transitions. Recently, the extended gaussian ensemble (EGE)
solution was obtained for this model. The gaussian ensemble and its extended
version can be considered as a regularization of the microcanonical ensemble.
They are known to play the role of an interpolating ensemble between the
microcanonical and the canonical ones. Here, we explicitly show how the
microcanonical energy equilibrium states related to the metastable and unstable
canonical solutions for the Blume-Capel model are recovered from EGE, which
presents a concave "extended" entropy as a function of energy.Comment: 6 pages, 5 eps figures. Presented at the XI Latin American Workshop
on Nonlinear Phenomena, October 05-09 (2009), B\'uzios (RJ), Brazil. To
appear in JPC
Overall evaluation of Skylab imagery for mapping of Latin America
The author has identified the following significant results. Skylab imagery is both desired and needed by the Latin American catographic agencies. The imagery is cost beneficial for the production of new mapping and maintenance of existing maps at national topographic series scales. If this information was available on a near time routine coverage basis, it would provide an excellent additional data base to the Latin American cartographic community, specifically Argentina, Bolivia, Chile, Colombia, Dominican Republic, Guatemala, Paraguay, and Venezuela
Amnestically induced persistence in random walks
We study how the Hurst exponent depends on the fraction of the
total time remembered by non-Markovian random walkers that recall only the
distant past. We find that otherwise nonpersistent random walkers switch to
persistent behavior when inflicted with significant memory loss. Such memory
losses induce the probability density function of the walker's position to
undergo a transition from Gaussian to non-Gaussian. We interpret these findings
of persistence in terms of a breakdown of self-regulation mechanisms and
discuss their possible relevance to some of the burdensome behavioral and
psychological symptoms of Alzheimer's disease and other dementias.Comment: 4 pages, 3 figs, subm. to Phys. Rev. Let
Spontaneous symmetry breaking in amnestically induced persistence
We investigate a recently proposed non-Markovian random walk model
characterized by loss of memories of the recent past and amnestically induced
persistence. We report numerical and analytical results showing the complete
phase diagram, consisting of 4 phases, for this system: (i) classical
nonpersistence, (ii) classical persistence (iii) log-periodic nonpersistence
and (iv) log-periodic persistence driven by negative feedback. The first two
phases possess continuous scale invariance symmetry, however log-periodicity
breaks this symmetry. Instead, log-periodic motion satisfies discrete scale
invariance symmetry, with complex rather than real fractal dimensions. We find
for log-periodic persistence evidence not only of statistical but also of
geometric self-similarity.Comment: 4 pages, 2 color fig
The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit
We use the results of a new, multi-epoch, multi-wavelength, near-infrared
census of the Trapezium Cluster in Orion to construct and to analyze the
structure of its infrared (K band) luminosity function. Specifically, we employ
an improved set of model luminosity functions to derive this cluster's
underlying Initial Mass Function (IMF) across the entire range of mass from OB
stars to sub-stellar objects down to near the deuterium burning limit. We
derive an IMF for the Trapezium Cluster that rises with decreasing mass, having
a Salpeter-like IMF slope until near ~0.6 M_sun where the IMF flattens and
forms a broad peak extending to the hydrogen burning limit, below which the IMF
declines into the sub-stellar regime. Independent of the details, we find that
sub-stellar objects account for no more than ~22% of the total number of likely
cluster members. Further, the sub-stellar Trapezium IMF breaks from a steady
power-law decline and forms a significant secondary peak at the lowest masses
(10-20 times the mass of Jupiter). This secondary peak may contain as many as
\~30% of the sub-stellar objects in the cluster. Below this sub-stellar IMF
peak, our KLF modeling requires a subsequent sharp decline toward the planetary
mass regime. Lastly, we investigate the robustness of pre-main sequence
luminosity evolution as predicted by current evolutionary models, and we
discuss possible origins for the IMF of brown dwarfs.Comment: 74 pages, 30 figures, AASTeX5.0. To be published in the 01 July 2002
ApJ. For color version of figure 1 and online data table see
http://www.astro.ufl.edu/~muench/PUB/publications.htm
The nature of the dense core population in the Pipe Nebula: A survey of NH3, CCS, and HC5N molecular line emission
Recent extinction studies of the Pipe Nebula (d=130 pc) reveal many cores
spanning a range in mass from 0.2 to 20.4 Msun. These dense cores were
identified via their high extinction and comprise a starless population in a
very early stage of development. Here we present a survey of NH3 (1,1), NH3
(2,2), CCS (2_1,1_0), and HC5N (9,8) emission toward 46 of these cores. An
atlas of the 2MASS extinction maps is also presented. In total, we detect 63%
of the cores in NH3 (1,1) 22% in NH3 (2,2), 28% in CCS, and 9% in HC5N
emission. We find the cores are associated with dense gas (~10^4 cm-3) with 9.5
< T_k < 17 K. Compared to C18O, we find the NH3 linewidths are systematically
narrower, implying that the NH3 is tracing the dense component of the gas and
that these cores are relatively quiescent. We find no correlation between core
linewidth and size. The derived properties of the Pipe cores are similar to
cores within other low-mass star-forming regions: the only differences are that
the Pipe cores have weaker NH3 emision and most show no current star formation
as evidenced by the lack of embedded infrared sources. Such weak NH3 emission
could arise due to low column densities and abundances or reduced excitation
due to relatively low core volume densities. Either alternative implies that
the cores are relatively young. Thus, the Pipe cores represent an excellent
sample of dense cores in which to study the initial conditions for star
formation and the earliest stages of core formation and evolution.Comment: 35 pages, 10 figures (excluding the appendix). For the complete
appendix contact [email protected]. Accepted for publication in ApJ
Contrasted land use and development trajectories in the brazilian Amazon.
A publicação traz resumo também em francês e espanhol
Avaliação de unidades demonstrativas do consórcio de amendoim com palma de óleo em áreas de produtores da agricultura familiar do sul do estado de Roraima.
Hadronic Masses and Regge Trajectories
A comprehensive phenomenological analysis of experimental data and some
theoretical models is presented here (for mesons) to critically discuss how
Regge trajectory parameters depend on flavor. Through analytic continuation of
physical trajectories (obtained from resonance data) into the space like
region, we derive the suppression factor for heavy flavor production. The case
of our D Regge exchange, both for D and production, is considered
in some detail. Good agreement with data is reached confirming that indeed the
slopes of heavier flavors decrease. This result suggests that the confinement
potential has a substantial dependence on the quark masses. In a simple
non-relativistic model, constrained to produce linear Regge trajectories, it is
shown that a linear quark mass dependence is required (in the confinement part
of the potential) in order for the slope to decrease in the appropriate way.Comment: 19 pages, 9 Figures, IV Table
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